1. Field of the Invention
The present invention relates to a fluid clutch, comprising a first transmission element and a second transmission element which is rotatable about an axis of rotation with respect to the first transmission element. Torque transmission surfaces of the first and second transmission elements are located opposite one another in a working fluid region in which torque transmission coupling between the first and the second transmission elements can be made selectively by means of fluid. A valve arrangement can be actuated for selectively making and breaking a fluid flow connection between a fluid storage region and the working fluid region, in order respectively to allow and prevent the ingress of fluid from the fluid storage region into the working fluid region, and a braking apparatus can generate a braking force acting on the second transmission apparatus.
2. Description of the Related Art
DE-G 89 08 359 discloses a fluid clutch, in which a transmission element carrying a dynamic-pressure pump can be braked by activating a braking apparatus. Activating the braking apparatus raises the relative rotational speed between the two transmission arrangements, so that the efficiency of the dynamic-pressure pump increases and therefore fluid is drawn off from the working fluid region to an increased extent. A permanently open orifice allows a fluid stream from the fluid storage region to the working fluid region is located between the working fluid region and the fluid storage region. The dimension of this orifice must be such that, on the one hand, a sufficiently rapid ingress of fluid into the working fluid region is possible, but, on the other hand, during the activation of the braking apparatus, outflow of fluid which would empty the working fluid region is prevented.
DE-G 89 08 357 discloses a fluid clutch which, in addition to an electromagnetically acting braking apparatus, has a further electromagnetic apparatus which opens and closes a valve arrangement to complete and interrupt the flow path between the fluid storage region and the working fluid region. Two separately actuated apparatus have to be provided here, which takes up a relatively large amount of construction space and, moreover, raises the outlay involved in activation during the changeover of this fluid clutch between various operating states.
The object of the present invention is to provide a fluid clutch, which, while having a simple makeup, allows a rapid and defined transition between various operating states.
This object is achieved by means of a fluid clutch comprising a first transmission element and a second transmission element which is rotatable about an axis of rotation with respect to the first transmission element. Torque transmission surfaces of the first and second transmission elements are located opposite one another in a working fluid region in which torque transmission coupling between the first and the second transmission elements can be made selectively by means of fluid. A valve apparatus can be actuated for selectively making and breaking a fluid flow connection between a fluid storage region and the working fluid region, in order respectively to allow and prevent the ingress of fluid from the fluid storage region into the working fluid region, and a braking apparatus can generate a braking force acting on the second transmission element.
This fluid clutch is defined by two components movable with respect to one another within a limited range of movement as a result of the transmission of braking force to the second transmission element. The valve element can be actuated for selectively making and breaking the fluid flow connection by means of a relative movement between the two components.
In the fluid clutch according to the invention, therefore, the braking force transmitted to or exerted on the second transmission element is utilized directly for actuating the valve apparatus, so that two reactions are triggered solely as a result of the initiation or activation of the braking apparatus. On the one hand, the second transmission element is braked and, on the other hand, the valve apparatus is initiated in order to modify the fluid flow connection between the fluid storage region and the working fluid region. This makes it possible, along with a very simple makeup, to have a very simple initiating operation.
For example, the valve apparatus may be assigned at least one actuating element which can move to make and break the fluid flow connection, and the at least one actuating element may be set in motion by means of a relative movement between the two components.
In order to obtain a defined interaction between the braking apparatus, which is to brake the second transmission element, and the valve apparatus actuated as a result of this braking force, a pre-stressing arrangement pre-stressing the two components into a basic relative position can be provided. The two components can be deflected out of their basic relative position, counter to the pre-stressing action of the pre-stressing arrangement, by means of a braking force which is to be transmitted. In this case, the at least one actuating element can be moved in order to actuate the valve apparatus during the movement of the two components out of the basic relative position.
In order to further simplify the arrangement, the at least one actuating element can be held movably on one of the two components, an interaction region can be provided on the other of the two components, which region is assigned to the at least one actuating element and acts on the at least one actuating element during relative movement between the two components. In this case, two components are preferably rotatable about the axis of rotation with respect to one another, and the relative rotational movement between the two components can be converted into a movement of the at least one actuating element. In this case, actuation of the valve arrangement can be obtained in a simple way by holding the at least one actuating element on the one component so as to move essentially in the direction of the axis of rotation, and the interaction region assigned to the at least one actuating element comprises a cam surface region on the other component.
In general, in a fluid clutch of this type, a state in which the braking arrangement is not activated is a state in which this clutch can transmit a torque and therefore the two transmission elements can rotate at essentially the same rotational speed. In this state, however, care must be taken to ensure that sufficient fluid is present in the region between the two transmission elements to obtain a sufficient shear action. The valve apparatus should therefore provide a fluid flow connection during the positioning of the two components in the basic relative position, and when the two components are deflected out of the basic relative position, the valve apparatus should be capable of being actuated for at least partially breaking the fluid flow connection when the two components are deflected out of the basic relative position.
In a simple arrangement which still permits a defined initiation of the valve apparatus as a function of the state of actuation or state of activation of the braking apparatus, the valve apparatus has at least one valve element pre-stressed into an opening position. When the two components are deflected out of the basic relative position, the at least one valve element can be moved toward its closing position by an associated actuating element.
It is also advantageous, at the same time, if, as a result of the pre-stressing of the at least one valve element into its opening position, the associated actuating element is pre-stressed into an actuating opening position or into interacting contact with the interaction region assigned to the latter.
In order to provide a sufficiently high braking action without any frictional force being generated, the braking arrangement can have an essentially fixedly positioned or positionable first braking region, which has an electromagnet arrangement for generating the braking force, and a second braking region capable of being brought into magnetic interaction with the first braking region.
Integration of parts or of functions may be obtained by the second arrangement region forming at least part of one of the two components or being connected thereto. Preferably, the second transmission element includes a housing which surrounds the working fluid region and forms at least part of one of the two components or is connected thereto.
Preferably, to build up or provide fluid circulation in the fluid clutch according to the invention, a pump arrangement, preferably a dynamic-pressure pump arrangement, is also provided, by means of which fluid can be conveyed out of the working fluid region into the fluid storage region.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.